A new method of measuring the dynamics of magnetization at arbitrary magnetic field is presented. It is illustrated by measuring the spin-lattice relaxation rate in paramagnetic Cdix Mn x Te in magnetic fields up to 25 T. At low fields, the spin-spin interaction of the Mn spins dominates the relaxation process; however, at high fields the relaxation of isolated spins can be observed. Among the spin clusters playing an important role as fast relaxation centers, exchange-coupled nearest-neighbor Mn pairs are identified, suggesting an important mixing of their states.PACS numbers: 75.20.-g, 76.30.Fc, 78.47.+p As a result of the presently available techniques, most of the experiments to study spin-lattice relaxation (SLR) are restricted to fields lower than a few tesla [1,2]. Unfortunately, at low magnetic fields, even for the most diluted magnetic systems, the interactions between spins of magnetic ions and also of uncontrollable impurities can strongly affect the relaxation [2], masking the isolatedspin behavior. However, at large enough magnetic fields, the mechansim of the relaxation becomes simpler since the interaction with the external magnetic field will be dominant, and the spin-spin interactions can be considered as negligible for the relaxation. Loosely speaking, the high magnetic field "purifies" the magnetic system, allowing studies of the isolated-spin relaxation. In addition, the relaxation rate for a multilevel system can be related directly to the transition probabilities between the levels at high magnetic fields only. This then allows the verification of possible theoretical models of SLR for such systems. Furthermore, one can expect that at high magnetic fields new relaxation processes could appear. For example, a simple theory [3] predicts that the relaxation with emission of two phonons could be important above about 20 T. This would manifest itself by a very strong magnetic field and a very weak temperature dependence of the SLR rates. Despite all these interesting questions, until now no detailed studies of spin-lattice relaxation in high magnetic fields and over a wide range of fields have been reported. In this work we developed a novel technique allowing studies of SLR in arbitrary fields. The technique has been illustrated by investigating SLR in the diluted magnetic semiconductor (DMS) Cdi-jcMn*-Te [4] for paramagnetic samples with compositions x between 0.002 and 0.05 [5] at magnetic fields B up to 24.5 T and at temperatures T between 2.6 and 10 K. We can conclude that at high fields single-spin relaxation is dominant for compositions x < 0.01. At lower fields the SLR is dominated by a channel given by the relaxation in spin clusters. The relaxation in exchange-coupled nearestneighbor (NN) pairs is clearly observed.The spin-lattice relaxation was measured with a timedomain magnetic spectrometer based on a pickup coil [6,7]. A pickup coil fixed around a paramagnetic sample with its axis parallel to an external magnetic field detects the externally induced changes of the longitudinal magne...

A time domain magnetic spectrometer based on a pick-up coil is presented for the study of spin-lattice relaxation rates in paramagnetic samples at high magnetic fields and at liquid-helium temperatures. The equilibrium between the spin system and the lattice is disturbed either by heating the spin system under the electron spin resonance condition (using far-infrared laser pulses) or by heating the lattice (using nonresonant laser pulses). Resulting magnetization changes induce a voltage in a pick-up coil oriented parallel to the field. By measuring the temporal evolution of this voltage, one can observe the spin-lattice relaxation directly. The spin-lattice relaxation in the diluted magnetic semiconductor CdMnTe is measured in order to demonstrate the performance of the spectrometer. The two methods of disturbing the equilibrium between the spin system and the lattice are compared.

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Improvements in the electrical and structural properties of tetraethylorthosilicate (TEOS) SiO 2 films fabricated by plasmaenhanced chemical vapor deposition (PECVD) method were investigated using high-pressure H 2 O vapor heat treatment. The density of interface trap states was reduced from 3:3 Â 10 12 (initial) to 5:1 Â 10 10 cm À2 eV À1 by 1:3 Â 10 6 Pa H 2 O vapor heat treatment at 260 C for 9 h. The density of fixed charges was also reduced from 6:1 Â 10 11 to 1:3 Â 10 11 cm À2. The full width at half-maximum (FWHM) of the optical absorption band corresponding to vibration of Si-O-Si bonding was reduced from 82.9 to 78.1 cm À1. Narrowing in FWHM of the Si 2p core level peak measured by X-ray photoelectron spectroscopy (XPS) was also observed. The reduction in the FWHM probably results from improvement of the Si-O bonding network.